Thermostat mechanism



DSC' 1, 1942- E. K. CLARK 2,303,911

V THERMOSTAT MECHANISM Filed Dec. 25, 1939 4 Sheets-Sheet 3 WITNESSES: 3/ INVENTOR ATTORN Y "DCQ L 1942- E. K. CLARK 2,303,911

THERMOSTAT MECHANISM O wlNEssEs: 13. INVENTOR Ear/ K. c/ark i ATTORN Y Patented Dec. 1, 1942 THERMOSTAT MECHANISM Earl K. Clark, Mansfield, Ohio, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.,.a corporation of Pennsylvania Application December 23, 1939, Serial No. 310,680

(Cl. 20o-140) 4 Claims.

My invention relates to thermostat mechanisms and has for an object to provide an improved mechanism of this kind.

A further object of my invention is to provide an improved thermostat of the expansible iiuid type wherein friction in the leverage system between the expansible element and the control means actuated thereby is maintained at a minimum.

A still further object of the invention is to provide improved apparatus of the character set forth which may be readily manufactured and calibrated, the adjusting member of all thermostats being uniformlypositioned relative the heatresponsive element and the control device actuated thereby.

It is a still further object of my invention to provide an improved thermostatic switch structure adaptable for two-pole construction and wherein creep action of the contacts is prevented during opening and closing movements thereof.

It is a still further object of my invention to provide'an improved thermostat of the fluid type for controlling the temperature of an oven wherein the bulb of the thermostat is rigidly positioned in the oven in a predetermined position and wherein damage to the capillary tube at the point where it enters the oven is prevented.

These and other objects are effected by my invention as will be apparent from the following description and claims taken in accordance with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is a partial front view of an electric range having my improved thermostatic control apparatus applied thereto;

Fig. 2 is a section taken on the line II-II of Fig. l;

Fig. v3 is a partial front View of another form of electric range having my improved control applied thereto;

Fig. 4 is a section taken along the line IV-IV of Fig. 3;

Fig. 5 is a sectional View taken on the line V--V of Fig. l;

Fig. 6 is a sectional view of a detail shown in Fig. 5;

Fig. '7 is a front view of the apparatus shown in Fis. 6;

Fig. 8 is a longitudinal sectional view of a thermostat constructed in accordance with my invention; i

Fig. 9 is a front view of the apparatus shown in Fig. 8 with portions removed for the sake of clearness;

Fig. 10 is a sectional view taken along the line X--X of Fig. 9;

Fig. 11 is a view of a detail shown in Fig. 8 looking from the plane XI-XI;

Fig. 12 is a longitudinal sectional view of a modified form of thermostat shown in Fig. 8 with parts removed for the sake of clearness;

Fig. 13 is a diagram of the spring forces of various elements shown in Fig. l2; and,

Fig. 14 is a wiring diagram for the oven element of the ranges shown in Figs. 1 and 3.

Reference will now be had to Figs. 1 and-2 wherein I have shown my improved thermostat applied to an electric range I0 having an oven portion II, and a cooking surface I2, the latter being provided with a plurality of surface heating elements, one of which is shown at I3. The range Il) includes a back splasher I4 which supports a plurality of switches I5, the latter controlling energization of their respective heating plates I3. The back splasher I4 also defines the support for the thermostatic control mechanism,l generally indicated at I6, and including a manually operated switch I'I and a thermostat IB, the latter being constructed in accordance with my invention. The manually operated switch I'I and the thermostat I8 are connected by a tie member I9 so that they define a unitary structure which is supported by the back splasher of the range. The construction of the thermostatic switch mechanism I8 and the manual switch I'I as a unit is described and claimed in a copending application of E. K. Clark and J. S. Wojcik, Serial No. 309,922, filed December 19,

' 1939 and assigned to the assignee of the present application.

As best shown in Fig. 2, both the manuallyoperated switch I1, which is of the rotary type, and the thermostat IB are actuated by a common knob 2|. Preferably, the knob ZI carries an uindex 20 which registers with indicia on the range, which indicia includes an off position and several temperature settings. A pulley 22 is rotatably mounted with the knob ZI and is connected by means of a belt 23 to a second pulley 24 carstat I8 which is connected in series with the switch I1 also energizes and deenerglzes the heating element automatically to provide a predetermined mean temperature within the oven. The electrical connections between the switch II, the thermostat I8 and the element Ila are clearly shown in Fig. 14 and need not be further described. It will be understood that the manual switch is open in the off position and is closed when the knob 2| is adjusted to any temperature position.

The thermostat I8 is of the hydraulic type and includes an expanslble element 28 formed of spaced flexible walls 21 secured at their peripheries and enclosing the intervening chamber 28 (see Fig. 8). The chamber 28 communicates by means of a capillary tube 29 with a bulb 3| disposed Within the oven II as best shown in Fig. 5. It will be apparent that the walls 2l of the expansible element 28 are closely spaced so that a small amount of fluid is contained therein; the major portion of the fluid being at all times contained Within the tube 29 and the bulb 3|. The disposition of the thermostat on the range I in both Figs. 1 and 3 is such that the expansible element 2B is not affected substantially by the heat of the oven or any extraneous source of heat, being at all times in an atmosphere whose temperature does not increase materially above that of the room in which the range is installed. As the variations in room temperature are relatively small, no compensation of the thermostat in response to such variations is necessary to provide the proper desired mean temperatures in the oven. In this connection, it will be understood that, where the expansible element is arranged so that transfer of an appreciable amount of heat from the heating elements of the range to the expansible element of the thermostat is effected, compensation of the thermostat must be provided. In accordance with this invention, I provide a thermal-responsive element wherein the amount of fluid ln the expansible element during periods of maximum oven temperature does not exceed of the total amount of fluid in the enclosed system. With this proportioning of the fluid in the enclosed system, very little change in the volume of the fluid because of ambient temperature changes is effected and, therefore, I have found that compensation of the thermostat for ambient temperature variations may be omitted.

Referring now to Fig 5, the numeral 32 indicates an oven lining surrounded by heat insulation 33, which oven lining 32 includes an end wall 34, at its rear side. An opening 35 is provided in the end Wall 34 through which the bulb 3l and the tube 29 are passed during their assembly to the oven lining 32. The bulb is secured to the side Wall of the oven lining 32 by means of brackets 36 which are arranged adjacent the side of the oven and in an upper region thereof, at which location the bulb 3| and the fluid contained therein quickly respond to temperature changes of the air Within the oven lining 32.

In accordance with my invention, a collar 3l is brazed or otherwise fixed to the tube 29 a predetermined distance from the bulb 3|. The collar 37 has relatively large end portions 38 and an undercut intermediate portion 39 which is adapted to rest on the bottom of the opening 35 formed in the oven liner 32. It will be understood that the opening 35 in the oven is sufficiently large to permit the passage of the bulb 3i and the inner enlarged end portions 38 of the collar 3l during assembly of the thermostatic bulb to the oven. After assembly, the plate 4I is secured to the end wall 34 in any suitable manner such as, for example, by means of a selftapping screw 42. The plate 4I closes the opening 35 and also bears on the collar 3l for maintaining it in fixed position. In accordance with this construction, the tube 29 is protected from injury during assembly or during operation. The collar 3l protects the tube 29 from abrasion or other mechanical injury which is possible where an unprotected tube is passed through an opening in the oven. It will be apparent from the foregoing description that the collar 31 not only protects the tube 29 which is usually formed of a soft material but also serves as an index for positively locating the bulb 3| in a predetermined location longitudinally within the oven.

IReference will now be had to Figs. 3 and 4 which showanother type of range having my improved thermostatic control mechanism applied thereto. The range I0 shown in Fig. 3 is somewhat similar to the range shown in Fig. 1 and includes an oven II, a back splasher I4 and a cooking surface I2, the latter serving to support the plurality of hotplates I3 in the same manner described heretofore. In this embodiment, the switches for controlling the hotplates I3 are shown at I5-and supported on a lower front wall 43 of the range. The thermostatic controlling mechanism, including a manually-operated switch 44 of the rotary type and a thermostatic controller 45 similar in construction to the thermostat I8, is arranged beneath the cooking top I2 and in line with the switches I5. As best shown in FigA, the switch 44 and the thermostat 45 are actuated to their various positions by a common operating knob 46 secured to the shaft 4`| of the switch 44. A second shaft 48 is connected by means of a coupling 49 to the shaft' 4I and is rotatable therewith, the shaft 48 including a bifurcated member 5I which extends within openings 52 formed in the rotatable member 53. The rotatable member 53 is connected to the adjusting stem 54 of the thermostat 45 for rotating the same during an adjustment of the thermostat. The rotatable member 53 may be formed as a pulley so that it can be used in conjunction with the bifurcated member 5I when assembled to a range in accordance with Fig. 3 or may serve as a pulley when used as shown at I6 in Fig. 2.

The thermostat 45 shown in Fig. 4 is secured by means of a bracket 55 to a wall member 56 adjacent the rear of the range I0 shown in Fig. 3, while the adjusting knob thereof is mounted exteriorly of the front panel 43 of the range. The thermostats 45 and I8 are of the same construction, so that a description of the thermostat I3 which appears hereinafter will suffice for both. The capillary tube 29 of the thermostat 45 may be extended to within the oven II in the same manner as described hereinbefore.

It will be apparent from an inspection of Figs. l to 4 that, in both embodiments, the thermostat mechanisms I 8 and 45 are remotely disposed both with respect to the oven and with respect to the surface plates I3; it being apparent that only the heat-responsive bulbs 3| are subjected to any source of heat. As set forth heretofore, no compensating provisions responding to ambient temperature changes are necessary as part of the thermostat structure.

Reference will now be had to Figs. 8 to 11, inclusive, wherein I have shown the switching and operating mechanisms of my improved thermostat which, it will be understood, is the same regardless of whether the thermostat is assembled to the back splasher of the range as shown in Fig. 2 or whether it is carried by a rear portion thereof'as shown in Fig. 4.

Referring particularly to Figs, 8 and 9, the thermostat I8 includes a body portion 51 preferably formed of molded insulating material. A supporting frame 58 is attached in any suitable manner to one side of the body portion 51 and serves to supvort the various movable elements in the thermostat to be described hereinafter. To the opposite side of the body portion 51 is secured a cover such as the tie member I9 when assembled, as shown in Fig. 2.

Thelower wall 21 of the expansible element 26 has a stud 6| secured to the central portion thereof, which stud is hollow and communicates with the tube 29. The stud 6| is supported by a cover 82 which is secured in any suitable manner, as for example, by means of screws 63 to the frame 58 and body portion 51. The chamber 28 within the expansible element 26, the hollow stud 6 I, the

tube 29 and the bulb or reservoir 3| define a closed chamber which is entirely illled with an expansible liquid, the volume of which increases and decreases with increases and decreases in temperature. Any suitable iluid may be employed which retains its liquidity up to temperatures of 600 F. or the maximum temperature at which the oven is operated.

The switching mechanism associated with the thermostatic structure I8 will now be described. This mechanism is best illustrated in Figs. 8 to 10, inclusive and is of the doublepole, doub1ebreak type. The switch mechanism includes in one pole thereof, a pair of stationary contacts 64 and 65, the former of which includes a longitudinally-extending portion 66 carried by the body 51 and positioned thereon by means of a rivet 68. The outer end of the longitudinallyextending portion 66 of the contacts 64 is provided with a' terminal screw 69 for connection to the electrical conductors. The contact 65 has a iongitudinally-extending portion 1| which overlies the portion 66 of the contact 64 and is insulated therefrom by means of an insulating strip 12. The contact portion 1| is provided with an eyelet 13 which. extends through openings in the conducting strip 12 and terminal portion 66 to r the lower side of the body 51 and is provided with a terminal screw 14 for connection to the electrical conductor. The eyelet 13 is insulated from terminal 66 by the base member 51 which may include a boss 15 that extendsinto an opening formed in the contact terminal portion 66. The opposite pole of the switching mechanism includes stationary contacts 16 and 11, which are connected to terminals in the same manner as described in connection with the contacts 64 and 65 so that a further description of the stationary contact structures 16 and 11 is deemed unnecessary.

Movable contacts 18 and 19 associated with the opposite poles of the switch are engageable with their respective stationary contacts. The movable contacts 18 and 19 are carried by an insulating bridge 8| which is disposed beneath a transverse strut 82, the latter being secured to the body 51 at its end by means of screws 83. The strut 82 carries a pair of stops 84 which are defined by studs 85 screwed into the strut 82 and locked in place by means of lock nuts 86, see Fig. 10. The studs 85 limit the upward movement of the bridge 8| and, therefore, the gap between 75 the movable contacts and their respective stationary contacts in switch-open position. As best shown in Fig. 10, the movable contacts v11 and 18 are closely carried by pins 81 which are driven into the insulating bridge 8| and permit limited rocking movement of the contacts 11 and 18 relative th'e bridge 8| in a plane longitudinal to the terminals 66 and 1|. Accordingly. good contact between the movable c'ontacts 11 and 18 and their stationary contacts is provided at all times.

Movement of the expansible member 26 is imparted to the switching mechanism by means including a plurality of levers which will now be described. 'I'he switch-operating leverage system includes a main switch arm structure 88 which includes a swivel 89 pivoted at 9| to arms 92 forming a part of the frame structure 58. 'I'he main switch arm 88 includes also a resilient switch arm 93 secured to the swivel 89 in any suitable manner, such as, for example, by rivets 94 and is provided at its free end with a pair of points 95, the latter being seated in indentations 96 formed in one leg of the spring 91 of U-shape as viewed in Fig. 8. The opposite leg of the spring 91 is provided with an indentation 98 for receiving an adjustably-pointed screw 99 carried by the frame structure 58.

As described more in detail hereinafter, the spring 91 functions as a snapover spring for effecting quick opening and quick closing of the switching mechanism. The pointed screw 99 is threaded into a plate |0| and locked thereto by means of a lock nut |02, the plate |0| being secured to the frame 58 by means of screws |03 which extend through elongated openings |04 formed in the plate |0|. In accordance with this construction, the plate I0| and the needlepoint screw 99 may be adjusted upwardly and downwardly for adjusting the relative amount of travel of the switch arm 88 each sideof its deadcenter position. The needlepoint screw 99 may be adjusted inwardly and outwardly relative to the plate |0| for varying the bias of the U- shaped spring 91.

Movement of the switch arm 88 is imparted to the insulated bridge 8| and the movable contact 18 by means of a link |05 loosely carried by the resilient arm 93. As shown, a pair of studs |00 extend through holes in the link |05 and position the same, which studs |00 are secured to the resilient arm 93 in any suitable manner. In accordance with this construction, limited movement of the link |05 relative to the arm 93 in switch-opening and switch-closing direction is provided. An upwardly-extending portion |06 is formed on the link |05 and extends into an opening |01 formed in the insulated bridge 8|, the upwardly-extending portion |01 having a suitable opening therein for receiving a pin |08 which is securely driven into the bridge 8|. The connection between the pin |08 and the portion |06 of the link |05 is such as to aiord some limited rocking motion of the bridge 8| relative the link 05 so that the pressures onthe movable contacts 18 and 19 are substantially equalized regardless of any inaccuracy in assembly of the apparatus.

The link |05 is biased toward the resilient arm 93 at all times by a-spring |09, one end of which bears against the resilient arm 93 and the opposite end of which rests on the seat formed on a stud IIZ, the latter extending through a suitable opening in the resilient arm 93 and being riveted or otherwise secured to the link |05. The spring |09 may be termed a follow spring which assures positive opening and closing of the switch contacts and prevents any creep action therebetween in the switch-closed position as shown in Fig. 8, the follow spring |08 is compressed and the resilient arm 88 engages a shoulder I I formed on the stud |2. The contacts are held closely in engagement by the bias of the spring 91 acting through the arm 98. The spring |09, in this position, impresses a slight bias upon the resilient arm 98 in switch-opening direction but it is relatively small compared to the force of the spring 81.

When the switch arm 88 is moved upwardly in switch-opening direction, the space between the link and the resilient arm 98 is first closed, and, after engagement of these elements, the switch is moved in opening direction. During the first portion of this movement, pressure is maintained between the movable contact and the stationary contacts by the spring |09. Acceleration of the lever 93 is rapid as described hereinafter as the space intervening between it and the link |05 is closed so that, after engagement of these elements, the movable contacts are disengaged from their stationary contacts in a snap-acting manner. It will be noted, that pressure between the movable and stationary contacts is maintained continuous by the spring |09 until the moment of separation. When actuated in the closing direction pressure between the movable and stationary contacts is established as soon as they engage, as the bias of the spring |09 is effective immediately upon separation of the link |05 and arm 93. Full pressure on the contacts is, of course, effective upon engagement of the arm 99 with the shoulder I0 of the stud ||2.

Movement of the expansible element 26 is imparted to the switch arm 88 through the medium of a lever ||3 pivoted at ||4 to arms ||5 carried by the frame structure 58. As best shown in Figs. 8 and li, the lever ||3 includes side portions ||8 having a web portion ||1 extending therebetween, the latter being engageable with one or more protuberances 8 formed on the underside of the switch arm structure 88. Preferably, the protuberances ||8 are formed by embossing the resilient arm 93 as shown. A center portion of the web ||1 is cut away as shown at ||9, the opposite sides of the cutaway portion ||9 forming knife edges |2| for a purpose to be described hereinafter.

Clockwise movement of the lever ||3 about its pivot ||4 effects counter-clockwise movement of the switch arm 88 about its pivot 9|, and vice versa, it being understood that the web |1 is maintained continuously in engagement with the protuberances 8. In this connection, a compression spring |22 is disposed between the swivel 88 and the fixed portion of the structure, for example, the body 51, for continuously biasing the switch arm 88 in clockwise or the switch-closing direction. In order to reduce to a minimum the amount of friction between the lever ||8 and the switch arm structure 88, I arrange their pivotal supports and the point of engagement of the web |1 and protuberances I8 in a straight line. Accordingly, these engaging members move substantially linearly and there is very little movement or slipping of the protuberances I8 relative to the surface of the web |1 duringmovement of the lever ||3.

Movement is imparted to the lever |8 through its knife edges |2| which bear upon spaced por- Hons of one side of a washer |23 that is carried by an adjusting stem |24, the latter being moved axially as the expansible element 25 expands and contracts. The stem |24 is threaded within a cup |25 which is welded or otherwise secured to a central portion of the upper diaphram 21 of the expansible element 28. A shoulder |2| is formed on the stem |24, preferably integrally, and functions as a stop for a second washer |21 carried on the stem |24 and juxtaposedwith respect to the washer |28. Both washers. |28 and |21 are DIO- vided with openings through which the stem |24 projects, said openings being somewhat oversize as to allow axial movement and limited rocking movement of the washers upon the stem. A relatively heavy compression spring |28 continually biases the stem |24 and the cup |25 apart, said spring bearing at one end upon'the washer |28 and its opposite end upon a fixed shoulder |28 formed on the cup |25.

In order that the pressure on the transverselyspaced knife edges |2| may be maintained substantially equal, I provide a pair of dlametricallyspaced protuberances III on the side of the washer |21 which is adjacent the washer |28. These protuberances bear upon the washer |28 and are spaced substantially from the point of engagement between the washer |28 and the knife edges |2|. Accordingly, any tendency of the washer |28 to bear unevenly upon the knife edges is counteracted by the protuberances III which permit slight rocking movement of the washer |28 in the plane of the knife edges. In order that the protuberances |3| remain substantially 90 from the knife edges |2|, a pair of ears |32 are formed on the washer |21 and extend in an axial direction alongside of the portion of the web ||1 which defines the knife edges |2|. This construction is best shown in Figs. 8 and 1l. Sliding of the knife edges |2| upon the surface of the washer |23 is minimized by arranging the pivot of lever ||8 in the plane of said surface of the washer |28 so that movement of the knife edges and the washer |28 is substantially linear.

Adjustment of the thermostatic structure is eiected by rotating the stem |24 or threading it inwardly and outwardly of the cup |25. These operations increase or decrease the distance between the washer |28 and the expansible element 26 so that more or less expansion is required to open and close the switch, depending upon the distance between these elements. Rotating the stem |24 to thread the same outwardly of the cup |25 increases the distance between the washer |28 and the expansible element 26 so that less expansion ofthe element 28 is required to operate the switch and, therefore, the switch is opened and closed at relatively low temperatures. Reducing the distance between the washer |23 and the element 28 necessitates greater expansion of the element 26 to operate the switch so that the oven is, therefore, operated at a relatively high mean temperature. It will be understood that the compression spring |28 is relatively heavy and sufcient at all times to overcome any bias imposed by the springs |22 and 91. Accordingly. the spacing of the washer |23 relative the element 25 is unchanged for a given adjustment during all normal operations. If, however, for any reason, the element 28 would continue to expand subsequent to a switch-opening movement of the mechanism, the compression spring |28 would compress somewhat in order to prevent any damage to the leverage system or the expansible elemen Expansion and contraction of the compression spring |28`is effected during periods of adjustment of the stem |24. When the mechanism is adjusted to a lower temperature setting from a higher temperature setting, during periods when the expansible element 26 is expanded, the switch would first be opened if in the closed position by the expansion of the spring |28 acting through -the leverage system. With the switch in the open position further adjustment of the stem |24 would move the shoulder |26 thereof away from the washer |23, it being understood that the lever I3 at this time -would prevent any axial movement of the washer |23. Contraction of the expansible element 26 would first engage the shoulder |26 and the washer |21 and, after engagement of these elements, would effect movement of the washer |23 and the leverage system. An adjustment of the mechanism from a lower temperature setting to a higher temperature setting compresses the spring |28. If the switch at this time is in the open position, it may be closed because of movement of the leverage system, the lever ||3 of whhich follows the washer |23 as it is moved axially. Further adjustment of the stem |24 with the switch closed would, of course, relieve the spring force in the leverage system to a value below that necessary to close the switch. Subsequent heating and expansion of the expansible element would increase the spring force in the leverage system sulciently to effect operation of the switch at the higher setting.

As set forth heretofore, adjustment of the mechanism vis eiected by rotating the stem |24. It will be apparent that'the means for turning the stem |24 must provide for axial movement as this stem is moved axially during operation of the thermostat and during an adjustment thereof. As shown in Fig. 8, the pulley 24 is employed for rotating the stem |24 and, accordingly, is loosely carried upon the stem |24 so that the latter may move axially relative the pulley. Rotation of the stem |24 is effected by a plurality of projections |33 formed on a surface of the pulley and disposed on opposite sides of a pin |34 which extends radially through the stem |24 and secured in position by means of a nut and lock washer construction |35. As the pulley 24 and the pro- Jections |33 rotate about the stem, the projections engage the pin |34 and effect turning of the stem |24. It will be apparent also that the pin |34 may move axially between the projections |33 at this time. Limited movement of the pulley 24 about its axis is provided by a stop |36 which is engageable with a projection |31 formed on the periphery of the pulley. The driving means for l"Serial No. 309,922, filed December" 19, 1939.

:Uniform adjustment of large numbers of thermostats in production may be effected by providing adjustment between the expansible element and the switching mechanism independently of the operators adjustment described heretofore. Accordingly, the expansible element 26 and the stud 6| thereof are rotatable in the cover 62 for providing axial movement of the stem |24 through its threaded connection to the cup |25.. 'I'he pin |34 may be held in a predetermined posi- -tion and the element 26 rotated for electiug operation of the switch at some predetermined temperature such' as the mid temperature in its operating range. The expansible element may then be locked in'place by a lock nut 1|50. All thermostats in production will, therefore, be uniform;

the position of their adjusting stems |24 relative the temperatures at which the switches are operated being identical for all thermostats.

As showny in Figs. 8 to 10, the thermostatic mechanism is in itsswitch-closed position and, therefore, heating of the oven is effected as the temperature of the oven and thetemperature of the fluid within the bulb 3| increase, the expanding fluid moves the stem |24 and the washer |23 axially so that the lever ||3 is moved in clockwise direction. Accordingly, the switch arm swivel 89 is biased in counter-clockwise direction in opposition to the bias of the springs |22 and 9|. All members of the movable elements are deflected including the expansible element 26, its adjusting screw assembly |24-|25, the lever i I3 and the switch arm structure 88 at this time. The increase in bias because of this deflection progressively increases.

At this time it will be understood that the resilient arm 93 is also biased toward the switchopen position by the follow spring |09. When the force developed in the spring arm 93 at the spaced points 96 is sufficient to overcome the bias of the U-shaped spring 91, movement of the resilient arm 93 to its switch-open position is initiated. Acceleration of the resilient arm 93 is rapid as the effective force or turning moment of the spring 91 is progressively reduced as it approaches its dead center position. The small bias imposed by the spring |09, of course, is renderedineifective when the resilient arm 93 engages the connecting link |05 but may be disregarded as it is of small value compared to the forces of the leverage system including the resilient arm 93 and the opposing force of the spring 91. The force at the spaced points 96 is reduced during this transition but it varies at a much lower rate than the reduction in force or turning movement of the spring 81. After passing through the dead center position, the spring 91 assists the resilient arm 93 in moving the switching mechanism to its open position. At the time of opening of the contacts, movement of the resilient arm 93, the connecting link |05 and the switch contacts is very rapid.

During the switch-open period, the temperature of the oven and of the fluid within the bulb 3| is reduced because of heat leakage from the oven, so that contraction of the uid within the thermostatic element is effected. Accordingly, the stem |24 and the washer |23 are moved downwardly because of the bias of the spring |22 which acts upon the washer through the main switch arm swivel 89 and the lever ||3. Movement of the swivel 89 in switch-closing direction increases the bias of the resilient arm 93 and, when 'the bias thereof overcomes the turning movement of the spring el, movement of the switch in closing direction is initiated.

As set forth heretofore, the turning moment of the spring 91 rapidly reduces as it approaches dead center, so that acceleration of the resilient arm 93 is rapid. The movable contacts of the switch at the time of closing are moving at high speed. After passing dead center, the resilient arm assisted b y the U-spring 91 continues its travel to the position shown in the drawings, duringwhich time the follow spring |09 is compressed. The pressure between the movable contacts and their respective stationary contacts is maintained substantially equal because of the loose connection between the insulating bridge 8| and the connecting link |05. Furthermore, as set forth heretofore, the contacts are always maintained under pressure when engaged at least to the extent of the pressure imposed by the follow spring |09. Creep action of the contacts is, l

therefore, precluded by the spring |09.

A further embodiment of the thermostatic switch structure is shown in Figs. 12 and 13. The thermostat, as shown in Fig. 12, is substantially the same as that shown in Fig. 8 and similar numerals for the common parts thereof are employed in both figures. The embodiment shown in Fig. 12 diiers from that shown in Fig. 8 in that the compression spring |22 is eliminated and the U-shaped spring 91 so positioned relative the pivot 9| of the main switch arm that it imposes a, bias at all times upon the resilient member 93 of the main switch arm 88 in switchclosing direction. In other words, the U-shaped spring 91 operates at all times on one side of its dead-center position.

The operation of the thermostat shown in Fig. 12 may be best understood by referring to the spring diagram of Fig. 13. It will be assumed that the switch shown in Fig. 12 is just closed and heating of the oven is initiated. At this time, the switch-opening bias of the leverage system including the resilient arm 93 is somewhat under three ounces, measured at the switch contacts, as shown at A in Fig. 13. The switchclosing bias of the U-shaped spring 91 is in excess of four ounces, as shown at B. The bias of the spring |09 is relatively small, of the order of one-third of an ounce, measured at the switch contacts, as shown at C. Of course, the bias of the spring |09 supplements the bias of the switch arm so that the total bias in switch-opening direction at this time is slightly over three ounces.

During the heating period, the leverage system is deflected and the bias of the resilient arm 93 increases to point D, at which time the combined bias of the resilient arm 93 and the spring |09 exceed slightly the bias of the spring 91, which is indicated at B. Accordingly, the main switch arm 88 initiates its'movement toward the switch-open position, the progressive vreduction in force imposed by the spring 91 being shown by the line E in Fig. 13. As the resilient arm 93 moves in switch-opening direction, its bias is reduced progressively, as shown by the line F. Midway of the switching gap, the resilient arm 93 and the connecting link |05 are engaged, as set forth heretofore, so that the bias imposed by the spring |09 is terminated, as shown at G on the diagram. At this time, however, it will be apparent that movement of the switching mechanism toward its open position is not substantially aiected, as the force imposed by the spring 91 is considerably below the force imposed by the main switch arm 88, as shown at H. Accordingly, the switch rapidly continues its movement toward the open position.

In the open position of the switch, the force imposed by the spring 91 is indicated at J on the diagram, while the force imposed in switchopening direction by the main switch arm 88 is shown at K. As the temperature of the oven decreases, the bias of the main switch arm structure 88 is progressively reduced from the point K to slightly below the point J on the diagram, at which time movement of the switch in closing direction is initiated. The force imposed by the spring 91 rapidly builds up While the bias of the main switch arm 88 increases at a lesser rate, so that the switch is rapidly accelerated during its movement to the switch-closed position. Midway of the switching gap, the bias of the spring |09 again becomes e'ective, as shown by the line L. In the closed position of the switch, the bias imposed by the main switch arm 88 is indicated at A and the force imposed by the spring 91 is indicated at B.

From the foregoing description it will be aP- parent that the spring 91 continuously biases, at all times, the main switch arm 88 in switch-closing direction and that the snap-acting movement of the switch is effected because of the rapid reduction or increase in the effective turning moment of the spring 91 during movements of the switch.

The specific spring values set forth in Fig. 13 is shown by way of example, and has been taken from tests conducted upon one switch constructed in accordance with my invention. The pressures referred to were taken at the switch contacts as a matter of convenience, and the corresponding pressures at the adjusting stem |24 are indicated in pounds at the right-hand side of the diagram |3. It will be apparent that a pressure of one ounce at the contact corresponds to a pressure of approximately 30 ozs. at the adjusting stem, which is a ratio of approximately thirty to one. It will be apparent that, for one unit ot movement at the expansible element 26, 30 units of movement are obtained at the switch contacts.

From the foregoing description it will be apparent that I have provided improved thermostatic apparatus of the expansible fluid type wherein the amplitude of movement of the switch is high relative the movement of the expansible element and wherein friction in the multiply- .ng leverage system is reduced to a minimum. The arrangement of the thermostat on the apparatus to be controlled and the construction of its expansible member are such that compensation for ambient temperature changes is obviated.

While I have shown my invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various other changes and modifications without departing from the spirit thereof, and I desire, therefore, that only such limitations shall be placed thereupon as are specically set forth in the appended claims.

What I claim is:

1. In a thermostat, the combination of an element movable in response to changes ln temperature, a switch actuated thereby, means for transmitting movement of the element to the switch and including a stem movable in an axial direction by the expansible element, an arm having a pivot, the axis of which is spaced from the axis of the stem and disposed substantially at right angles thereto, said arm having a pair of laterally-spaced knife-edge portions, a collar having a surface extending substantially normal to the axis of the stem and engageable with the knife-edge portions of said arm, said collar being arranged substantially coaxial with respect to the stem, and means for positioning the collar upon the stem and affording limited rocking movement of the collar relative to the stem, whereby the pressures between the knife edges and the respective portions of the collar engaged thereby are maintained substantially equal.

2. In a thermostat, the combination of an element movable in response to changes in temperature, a switch actuated thereby, means for transmitting movement of the element to the switch and including a stem movable in an axial direction by the expansible element, an arm have ing a pivot spaced from the axis of the stem and extending substantially at right angles thereto, a shoulder carried by the stem, a collar engageable with the shoulder and having spaced protuberances formed on a face thereof, asecond collar carried by the stem, means for biasing said second collar into engagement; with said protuberances, said arm having a pair of laterallyspaced knife-edge portions engaging portions of the second collar, and means for maintaining said protuberances aligned substantially at right angles to a line extending through said knife edges.

3. In a thermostat, the combination of a iluidcontaining element having a diaphragm portion movable in response to temperature changes, an intemally-threaded cup secured to the diaphragm and movable in an axial direction therewith, a stem threaded within the cup, a shoulder carried by the stem, a rst washer slidably carried by the stem and engaging said shoulder, said washer having a pair of spaced protuberances carried on a face thereof, a second washer slidably andloosely carried by the stem, said second washer having a face thereof engaging said protuberances whereby limited rocking of the second washer upon the protuberances is afforded, biasing means interposed between said cup and the second washer, a switch, means for transmitting movement of said diaphragm to the switch and including a pivoted arm having spaced knife-edge portions in engagement with spaced regions of said second washer, and means for rotating the stem for adjusting the temperatures at which the fluid-containing element operates the switch` 4. In a thermostat, the combination of a wall member having an opening therein, a control device, a uid-containing heat-responsive element for actuating said control device and arranged on one side of the wall member, said heatresponsive element including a capillary tube extending through said opening and an elongated bulb, means for positioning said bulb on the opposite side of the wall member, a sleeve fixed to said tube a predetermined distance from said bulb, said sleeve having a portion thereof resting upon a side of the opening in the wall member, and a clip secured to the wall member for closing the opening therein and engaging said portion of the sleeve, whereby movement of the sleeve within the opening is prevented.

EARL K. CLARK. 

